Process for treating aluminum to provide selective coloration of portions thereof



T May 22, 1951 v. E. LEWIS ETAL 2,554,256

PROCESS FOR TREATING ALUMINUM To PROVIDE SELECTIVE COLORATION 0F PORTIONS THEREOF Filed May 15, 1948 fllz/mi/zum Elan/f e j.

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ATT RNEY Patented May 22, 1951 UNITED STATES PATENT OFFICE :P-R/OGESSv FOR TREATINGeALUMINUM .TO -PROVIDE SELECTIVE,COLORATION OF PORTIONS THEREOF Virginia E. Lewis and William EfCollar, Lima,

Ohio, assignors to Westinghouse Electric Corporation, East PittsburghgPa a corporation of Pennsylvania Application May. 15, 1948,Se"rial No. 27,328

v6 Claims. 1 This invention relates to the treatment of aluminum members to provide for preferentially 'coloringselected portions of the surfaces theremental and instructional members are required to have indicia or markings of the high contrast for ease in' reading and visibility.

'I-Ieretofore, processes consisting of a plurality of complicated steps have been known to the art for treating aluminum in such a manner as to provide indicia or markings thereon, but the steps "were lengthy and required considerable care in processing to prevent smearing of 'various' coloring agents. "These priorart processes required considerable skill on the part of the worker and slight deviations would result in unsatisfactory work.

The object of this invention is toprovide a rela- -tively simple .process for preferentially coloring selected portions of the surfaces of aluminum members.

"Other ob'jects'of the invention will in :partrbe obvious and will in: part appear. hereinafter.

For a better understanding Oflithe'i nature and objects of the invention, vreference should be had to the ':following 'detailedidescription .and

drawing, in which:

Figure 1 is aview inelevation ofan aluminum blank;

Figs. 2 and 3 are-viewsshowing theplan and cross-section on' Iine'IIII- III of Fig. 2, respectively; through a coined aluminum plate;

Fig.4- isa 've'rtical cross-section; Fig. 5 isavertical cross-section; Fig. 6'is--a vertical cross-section; and

Fig; 7 is a vertical cross-section through afinished aluminum plate.

It has been discovered that aluminumand aluminum alloy-members maybe colored: adeep contrasting black by abrading any desiredportion'thereof to expose fresh' aluminumandapplyingtosuch abraded surfacesan aqueous solution containingas its essential ingredients Ebetween 1 to 120 grams per liter of ammonium molybdate and between 1 to 128 grams per liter of ammonium chloride. Optionally there may be added to the solution from 1 to 100 grams per liter of an acetate selected from the group consisting of sodium acetate, potassium acetate and ammonium acetate in order to increase the blackening effect. Thesolution is applied hot, preferably boiling, in order -to-secure the most rapid blackening effect. Aslittle as-30 seconds in the solution-produces a desirable coloration, from 1 to 3 minutes giving the optimum results and as much as 10 minutes applicationof the solution has given satisfactory results. Only the freshly abraded aluminum surfaces react with the solution; while the unabraded surfacesremain substantially unaffected.

Abrading of the aluminum surfaces may be accomplished in various ways-asby applying a mask to an aluminum plate and abrading the surfaces exposed through the mask with a sand blast, 'Wire wheel or sand paper. .The most desirablemethod for many purposes .is to depress the portions of the surface of the member by coining, milling or other operation and then to sand or otherwise remove the surface layer from the relief surfaces thus to provide a fresh aluminum surface. Aluminum trimior strip: and aluminum extrusions having relief surfacesmay be,

:and often are, produced?duringimanufacture and "no additional "mechanicalrelief surface forming OperatiOnsJare'i requiredv for the practice of the present process. .iThe reliefs'surfaces in such cases may be readily sanded or ground or. milled to remove the'surface layer; thereby exposing the reactive fresh" aluminum. it is "believed that the surface layers contain "oxides and aluminum metal whichis non reactive with the aqueous compositions of this inventionzand their removal exposes fresh reactive metal. Only a'very thin layer'of: the. order of 0.0001ito 0.001 inch need be 'removedito expose the .fresh aluminum. Obviously. much more'xmay': be' removed.

,' For thepractice of .thisinvention-both commercially pure aluminum and aluminum alloys containing per cent or morealuminum may betreated. ".The'term aluminum as'employed herein is intended torcover' bothpurealuminum and the: commercial i alloys thereof containing silicon, zinc,magnesium,'manganese, copper and the like, and the balance, 90% orimore, aluminum.

The process of'ithisiinvention hasigiven particularly good resultsin' making aluminum name plates. Referring to' thefigurespf .the drawing, there is illustrated the .consecutiveiser-ies .of'steps for treating an aluminum blank to produce therefrom an aluminum name plate having depressions of the normal silvery aluminum color and relief portions colored a dark contrasting black. The aluminum blank I in Fig. 1, which may be of any suitable thickness, size and shape, may be coined in a press to produce the reliefbearing plate [2 shown in Figs. 2 and 3 of the drawing. The coined plate I2 comprises depressed portions l4 and relief portions l6. Since the coined plate l2 may be covered with grease and other soil acquired before and during coining which may interfere with subsequent treatment, it is desirable to clean the coined blank l2 as shown in Fig. 4 of the drawing. The coined plate 12 is put into a tank [8 containing a solvent 20 for grease and other solvent soluble soil thereon. It will be understood that several cleaning steps may be required to properly clean the plate. Vapor de-greasing systems may be employed or any other suitable cleaning processes known to the art. However, the cleaning process should not remove the surface layer in the depressed portions l6 or alter it chemically to any appreciable depth.

The cleaned plate I2 is then abraded as illustrated in Fig. by a sanding wheel 22 for removing from the relief surfaces the thin surface film thereby exposing fresh reactive aluminum metal at the surfaces l5. It will be clear that not all of the relief surfaces need be abraded. Thus, only a part of the surface may be abraded if it is desired only to color such selected part.

Thereafter, the aluminum plate l2 with the abraded surfaces I6 is immersed in the blackening solution 24 as disclosed herein contained in a tank 26. The solution is heated by the steam pipes 28 to keep it at or near the temperature at which it boils. After 30 seconds to minutes immersion in the solution 24, the plate I2 is removed and is preferably rinsed in cold water to wash off the solution 24. To improve the corrosion resistance of the aluminum, the plates may be further dipped in a solution of a dichromate selected from the group consisting of sodium dichromate and potassium dichromate. Aqueous solutions containing from one ounce to fifty ounces per one hundred gallons of the dichromate, preferably hot, may be employed. As shown in Fig. '7 of the drawing, the finished plate l2 exhibits a blackened relief surface 30 resulting from the treatment. The black color is permanent and will withstand normal wear and tear and chemical attack from atmospheres to which it may be subjected. The contrast between the blackened surfaces 30 and the natural silvery color in the depressed portions l4 renders the name plates extremely legible and visible at a considerable distance.

In some cases it may be desirable to apply a paint or coloring material to the depressions M which will contrast with the black relief surfaces 30 produced by the practice of this invention. In this case, the coined blank l2 as shown in Figs. 2 and 3 of the drawing may be sprayed or dipped in a paint and baked to cure the paint, or it may be subjected to an anodizing and dyeing treatment to produce a colored surface in the depressions l4. During subsequent sanding by the drum 22 the relief surfaces [6 will be cleansed of any paint or dye present thereon exposing fresh aluminum at such surface. The chemical treatment in the solution at will not impair such paint or dye in the depressions I l. Thereafter the name plate will exhibit portions of contrasting color to suit requirements. If desired, only a part of the depressions in a name plate may be dyed and the others left uncolored for the purpose of securing certain effects. Masks and the like may be employed for this purpose. However, the process shown in Figs. 1 to 6 of the drawing is extremely simple and requires the minimum of skill and care and ordinarily will suit most needs. It produces extremely dependable results.

We have found particularly good results to be secured by employing solutions 24 having the following composition:

Grams per liter Ammonium chloride 5 to 30 Ammonium molybdate 3 to 15 sodium acetate 5 to 15 Aqueous solutions of this composition when applied to a freshly abraded aluminum while at their boiling temperature give a dark, deep black coloration in from 1 to 3 minutes upon all freshly abraded aluminum surfaces. This solution has been effective on plates that have been cleaned and abraded as long as 15 hours previous to immersion. Abraded surfaces may be heated for a few minutes up to 300 C. without changing the reactivity with the solution.

If desired for the maximum protection, the aluminum members treated in accordance with the invention may be coated with a transparent organic finish such, for example, as cellulose acetate, ethyl cellulose, nitrocellulose lacquers and the like. The aluminum plates may be imbedded by impressing them into sheets of softened transparent plastic such, for example, as films of polystyrene, cellulose acetate and ethyl cellulose. The distinct coloration of the aluminum will be easily apparent through the plastic films and the utmost in resistance to wear and tear will be secured by such combinations.

Since certain obvious changes may be made in the above processes, and different embodiments of the invention could be made without departing from the scope thereof, it is intended that all material contained in the above description or taken in connection with the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

We claim as our invention:

1. In the process of preparing an aluminum member with markings of contrasting coloring thereon, the steps comprising providing an aluminum member having no surfaces that have been exposed to air for less than 15 hours, abrading a portion of the aluminum member to remove a surface layer, applying to the aluminum member, within 15 hours after abrading and without exposing the abraded surface to temperatures of above 300 0., a hot aqueous, non-alkaline solution comprising as its essential ingredients from 1 to grams per liter of ammonium molybdate and from 1 to 128 grams per liter of ammonium chloride, for at least 30 seconds and not exceeding 10 minutes to blacken only the abraded surfaces whereby to provide said markings.

2. In the process of preparing an aluminum member with markings of contrasting coloring thereon, the steps comprising providing a depression in the aluminum member, exposing the surfaces to air for more than 15 hours, abrading the relief portion of the aluminum member to remove a surface layer, applying to the aluminum member, within 15 hours after abrading and without exposing the abraded surface to temperatures of above 300 (3., a hot aqueous solution comprising as its essential ingredients from 1 to 120 grams per liter of ammonium molybdate, from 1 to 128 grams per liter of ammonium chloride, and an acetate selected from the group consisting of sodium acetate, potassium acetate and ammonium acetate, for at least 30 seconds and not exceeding minutes to blacken only the abraded surfaces whereby to provide said markings.

3. In the process of preparing an aluminum member with markings of contrasting coloring thereon, the steps comprising providing a depression in the aluminum member, the surfaces of the aluminum member after depression being exposed to air for more than hours, abrading the relief portion of the aluminum member to remove a surface layer, applying to the aluminum member, within 15 hours after abrading and without exposing the abraded surface to temperatures of above 300 0., a hot aqueous solution comprising as its essential ingredients from 1 to 120 grams per liter of ammonium molybdate, from 1 to 128 grams per liter of ammonium chloride, and an acetate selected from the group consisting of sodium acetate, potassium acetate and ammonium acetate, for at least 30 seconds and not exceeding 10 minutes to blacken only the abraded surfaces, and applying an aquous solution of a dichromate selected from the group consisting of sodium dichromate and potassium dichromate.

4. In the process of preparing from flat aluminum stock an aluminum member bearing selected markings of contrasting coloring, the surfaces of the flat aluminum stock having been exposed to air for substantially more than 15 hours, the steps comprising coining a flat surface of the aluminum stock to provide relief portions, without exposing any substantial amount of fresh aluminum at the surfaces, cleaning the coined member to remove any grease and other soil from the relief portions, abrading the relief portions of the member to expose fresh aluminum, immersing the abraded member, within 15 hours after abrading and without exposing the abraded surface to temperatures of above 300 0., for a period of from 30 seconds to 10 minutes in a boiling solution composed of from 3 to 15 grams per liter of ammonium molybdate and 5 to 30 grams per liter of ammonium chloride whereby the abraded relief portions only are blackened, rinsing the aluminum member with water and applying to the member an aqueous solution of a dichromate selected from the group consisting of potassium dichromate and sodium dichromate.

5. The process of preferentially coloring selected portions of aluminum members all of whose surfaces have been exposed to air for more than 15 hours, the steps comprising abrading the selected portions to remove a surface layer, and applying to the abraded portions, within 15 hours after abrading and without exposing the abraded surface to temperatures of above 300 C., a hot aqueous, non-alkaline solution composed of from 1 to 120 grams per liter of ammonium molybdate and from 1 to 128 grams per liter of ammonium chloride for from 30 seconds to 10 minutes.

6. The process of preferentially coloring selected portions of aluminum members all of whose surfaces have been exposed to air for more than 15 hours, the steps comprising abrading the selected portions to remove a surface layer, applying to the abraded portions, within 15 hours after abrading and without exposing the abraded surface to temperatures of above 300 0., a hot aqueous solution composed of from 1 to 120 grams per liter of ammonium molybdate and from 1 to 128 grams per liter of ammonium chloride, and from 1 to grams per liter of an acetate selected from the group consisting of sodium acetate, potassium acetate and ammonium acetate for from 30 seconds to 10 minutes.

VIRGINIA E. LEWIS. WILLIAM E. COLLAR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 567,926 Strecker Sept. 15, 1896 1,384,033 Norton July 5, 1921 1,551,613 Pacz Sept. 1, 1925 1,838,633 Pacz Dec. 29, 1931 2,312,855 Thompson Mar. 2, 1943 

5. THE PROCESS OF PREFERENTIALLY COLORING SELECTED PORTIONS OF ALUMINUM MEMBERS ALL OF WHOSE SURFACES HAVE BEEN EXPOSED TO AIR FOR MORE THAN 15 HOURS, THE STEPS COMPRISING ABRADING THE SELECTED PORTIONS TO REMOVE A SURFACR LAYER, AND APPLYING TO THE ABRADED PORTIONS, WITHIN 15 HOURS AFTER ABRADING AND WITHOUT EXPOSING THE ABRADED SURFACE TO TEMPERATURES OF ABOVE 300* C., A HOT AQUEOUS, NON-ALKALINE SOLUTION COMPOSED OF FROM 1 TO 120 GRAMS PER LITER OF AMMONIUM MOLYBDATE AND FROM 1 TO 128 GRAMS PER LITER OF AMMONIUM 